Choosing an SD card¶
In over 95% of “Armbian won’t boot” or stability reports, the cause is the SD card or the power supply — not the board and not the image. Armbian cannot run reliably on unreliable storage, so the card you pick matters as much as the board itself.
Why the card matters¶
A single-board computer uses the card as its system disk: constant small, random reads and writes, not the large sequential transfers a camera makes. The familiar speed class (Class 10, U1/U3, V30) only rates sequential throughput. What actually matters for an operating system is random IOPS, which the SD Association rates separately as the Application Performance Class — A1 and A2.
| Application Performance Class | Min. random read | Min. random write | Min. sustained sequential write | |
|---|---|---|---|---|
| Class 1 (A1) |  |
1500 4K IOPS | 500 4K IOPS | 10 MB/s |
| Class 2 (A2) |  |
4000 4K IOPS | 2000 4K IOPS | 10 MB/s |
What to buy¶
Pick a card that is:
- A1 or A2 rated. A2 is not slower or less supported than A1 on Armbian — where an A2 card’s command-queuing feature isn’t used it simply behaves like an A1, never worse. Either rating is fine; A2 is the safer target when buying new.
- at least UHS-I, U3 / V30 — the faster sequential write also speeds up flashing and large writes.
- 32 GB or larger — small cards wear out sooner, and images plus updates need the room.
- from a reputable brand. A1/A2 cards are not exclusive to any single manufacturer: Samsung, SanDisk, Lexar, Kingston and others all make suitable A1/A2 cards. Choose a well-reviewed model from a trusted seller.
For 24/7, logging-heavy, or write-heavy use, a high-endurance card (the kind marketed for dashcams and CCTV) lasts far longer than a standard consumer card.
Avoid:
- SD Express cards — an SD Express card also carries a legacy SD/UHS-I interface, so it still works in an ordinary reader, but most SBC readers can’t use its PCIe/NVMe path, so you gain nothing over a good UHS-I card. Buy one only if your board documents SD Express support.
- No-name or suspiciously cheap cards and unfamiliar listings — counterfeits are common (see below).
Further reading
The community-maintained SwitchRoot SD card guide has current, brand-by-brand benchmarks and a list of cards to avoid. Its rankings, benchmarks and compatibility notes are measured on the Nintendo Switch (DDR200, hekate) and do not necessarily carry over to Armbian boards or readers — treat them as a starting point, not verdicts for your hardware. Its counterfeit-card advice, however, applies anywhere.
Check the card before you trust it¶
Counterfeit and failing cards are the single most common cause of boot and corruption problems. Verify every new card — and any card you suspect — with:
Both fill the card and read it back, so test an empty card and back up anything on it first (H2testw’s full test needs the card formatted). This detects a fake that reports false capacity and surfaces read/write errors — do it right after purchase so you can refund a bad card before you rely on it. It cannot guarantee a genuine card won’t fail later.
Reusing an old card¶
A card that has been used before may have degraded write performance. Before writing Armbian, run the SD Association’s SD Memory Card Formatter — it rewrites the card with the SD-optimized filesystem and alignment it expects, which can help (background). If the card is still slow or reports errors afterwards, replace it.
Once you have a good card, continue with writing the image.